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Since 1624 it's been illegal for MPs to resign, so Hunt had to be given one of two ceremonial jobs that disqualify him - Steward and Bailiff of the Chiltern Hundreds or Steward and Bailiff of the Manor of Northstead. He was appointed to the Three Hundreds of Chiltern.

Because it was a Labour seat, Labour's House of Commons whips (with the leader's office) got to decide when to move the "writ" that triggers a poll.

Why is it a test for Labour?

(Image: Christopher Furlong)

Labour have held Stoke constantly since the 1950s - but over the last 20 years, their majority has shrunk dramatically.

In 1997, they won by 19,924 votes.

But their majority in 2015 was just 5,179 - 39.3% of the vote.

Ukip came second, on 22.7% of the vote, and this time they've got a much more high profile candidate in party leader Paul Nuttall.

Secondly, it's reputed to have exactly the northern Labour voters that Corbyn's critics would tell you he's alienating. It's an ex-industrial town with higher than average unemployment - and it voted 70% to leave the EU, which makes it a target for Ukip.

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Who are the candidates?

Labour - Gareth Snell

(Image: Daily Mirror)

Gareth Snell is a local councillor and former leader of Newcastle-Under-Lyme council. He campaigned for Remain during the referendum.

He recently apologised to his family for some old tweets that were unearthed where he described panelists on ITV's Loose Women as “squabbling sour-faced ladies”, and called Janet Street-Porter as a “polished turd”.

Ukip - Paul Nuttall

Paul Routledge out and about in the Stoke constituency (Image: Daily Mirror)

Paul Nuttall has been Ukip leader since taking over from Nigel Farage in November.

When he took over, he immediately promised to target the Labour heartlands.